Understanding Immunity To Tick Borne Diseases In Cattle

The livestock disease, epizootic bovine abortion (EBA) also known as foothill abortion, can cause significant economic losses to beef cattle producers in the state of Nevada, as well as producers in California and Oregon. Many of the regions of Nevada where beef cattle production occurs are also the home of the tick, Ornithodoros coriaceus, which transmits the bacteria that causes foothill abortion. Infection with this disease can lead to large numbers of late-term abortions in effected cattle herds.

Currently beef cattle producers in the areas where EBA is prevalent can only avoid loss due to this disease by placing heifers or cows onto rangeland containing the tick vector prior to pregnancy in order to expose them to infection. This method of disease management can result in large losses if susceptible pregnant cattle are inadvertently placed on these rangelands.

This project measures the duration of immunity against this disease after an initial EBA induced abortion by infecting a herd of susceptible heifers and exposing them to subsequent experimental infection over a five year period.

The results of this research will provide cattle producers and veterinarians with scientifically validated information on the length of time that cattle are resistant to this disease for use in their cattle management decisions. The results of this project will also be of great value in the potential development of a commercially available vaccine against this important disease.

Ranching and livestock grazing in the western United States have been an integral part of the economic and cultural landscape of the region since western expansion by European colonists. Today beef cattle production remains an important component of the economy of most western states. Within the states of California, Oregon, Nevada, and Idaho, beef cattle sales accounted for over $3.5 billion in revenue in 2005, and comprised nearly 10% of the states’ revenue for all agricultural commodities combined (Traub, 2006). Since profits are dictated by the weight and number of the animals sent to market by the producer, diseases which affect the reproductive health of cattle often result in considerable economic loss. Depending on the severity of an EBA outbreak, the death of replacement animals can force a producer into a difficult economic situation, including the potential loss of their livelihoods.

The bovine disease, epizootic bovine abortion (EBA), commonly referred to as foothill abortion, can result in the loss of up to 60% of the calf crop in an affected herd (Schmidtmann et al., 1976; Storz et al., 1967). This disease can result in large economic losses for beef cattle producers in northern Nevada, southern Oregon, Idaho and the mountainous regions of California. Abortion due to EBA results in an estimated loss of 5-10% of the beef calf crop and millions of dollars in lost revenue annually in California alone (Maas, 1995). The disease has been reported in cattle herds throughout Nevada including Elko County and the counties adjacent to the eastern front of the Sierra Nevada mountain range (Hall et al., 2002). These regions are also where the majority of the cattle herds in the state are raised. Current agricultural statistics indicate that EBA is considered one of the 5 most important livestock diseases in Nevada.

Epizootic bovine abortion is an infectious, bacterial disease characterized by late-term abortions in susceptible cattle grazing in geographic regions where the disease is endemic. Abortions due to EBA often occur in herds with large numbers of susceptible animals; these include pregnant heifers or cows in their first grazing season that are introduced into areas harboring the vector, Ornithodoros coriaceus. This argasid tick is the only known vector of EBA and the distribution of the disease is congruent with the distribution of O. coriaceus (Furman and Loomis, 1984). The incidence of EBA outbreaks in western states appears to be intimately tied to the distribution and density of O. coriaceus populations in the habitats in which cattle graze. Epizootic bovine abortion is most commonly associated with heifers or susceptible, older cows that have been exposed to the bite of a tick infected with the agent of EBA in the early stages of pregnancy, typically at 90 to 120 days of gestation (Stott et al., 2002). Cows that have aborted a fetus following an EBA infection do not abort upon subsequent exposure to infected tick bites, but the duration of immunity to EBA after natural exposure is unknown and appears to wane without repeated exposure to the agent through infected tick bites (BonDurant and Anderson, 1997). The lack of a vaccine against this disease and the lack of an antemortem test to detect previous exposure to the disease has forced beef cattle producers in areas where EBA is endemic to “manage around” the disease for decades in order to avoid losing calves due to abortions. The lack of a protective vaccine or diagnostic test to identify infected animals has forced beef producers to make management decisions based on subjective information, thereby increasing the chances for an outbreak in the herd.

Determine the basic physiological, immunological, metabolic and genetic systems that contribute to optimum reproduction in domestic ruminants with emphasis on gonadal development and function, establishment of pregnancy, placental function and fetal development, pubertal, and seasonal and post-partum anestrus.

Develop tools, techniques and management strategies to allow producers to control reproductive efficiency, including development of markers for reproductive health and disease, and chemical and immunological means of detecting and regulating fertility.